The present invention relates generally to sealing assemblies for rotary machines and, more particularly, to a sealing assembly for a steam or gas turbine.
Rotary machines include, without limitation, steam turbines, compressors and gas turbines. A steam turbine has a steam path that typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path, which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
To reduce gas and steam-path leakage in gas and steam turbine engines, labyrinth sealing assemblies are used. In steam turbines a sealing assembly having caulked-in sealing strips, which are disposed between rotary and stationary components of the turbine engine, is often employed. Such a sealing assembly, however, requires a trade-off between turbine efficiency and sealing assembly integrity. For example, the effectiveness of the sealing assembly depends significantly on maintaining a desired clearance between the sealing strips and the rotary component positioned radially opposite thereto. Exceeding the desired clearance degrades the efficiency of the turbine engine. However, under certain circumstances, for example during transient and startup conditions, the rotary component may be displaced from its normal position, causing the rotary and stationary components to interfere. As a result, the sealing strips rub against the rotary component, potentially damaging the sealing strips. Thus, in order to maintain the sealing assembly integrity, a larger than desired sealing assembly clearance may be necessary, which in turn reduces the efficiency of the turbine engine. Present techniques used to compensate for greater clearances between rotary and stationary components include altering the configuration of the interfering surfaces with integral machined rails or teeth. However, such techniques are expensive to implement and may require replacement of the rotary components in the event of damage to the machined tooth under unpredictable transient behavior.
Accordingly, it would be desirable to develop a cost effective sealing assembly that permits tight clearances, without impairing the performance of the sealing strips because of any damage during transient rubs.